1. Field of the Invention
The invention relates to a hydraulic device for the automatic connection of a pressure means source, dependent on the pressure in the circuit of a primary user, either preferably with the primary user or with a secondary user.
2. Brief Description of the Background of the Invention Including Prior Art
A device of the kind recited above is known from the German Printed Patent Application DE-OS 3,347,637. The device taught in the German Printed Patent Publication DE-OS 3,347,637 includes a switch valve of the kind of a pressure balance, by way of which the pressure means source can be connected or, alternatively, blocked relative to the secondary user.
In case of blocking of the pressure means source versus the secondary user, the pressure means source is predominantly connected with the primary user. The actuation of the switch valve is performed with the aid of a precontrol pilot valve, controllable with the pressure of the primary user. A pressure control chamber of the switch valve is connected either with the pressure means source or with a pressureless storage container.
The switching from one switching position into a second switching position is to occur rapidly and quickly, i.e. it is to be avoided that an unstable switching state occurs during a critical pressure phase in the primary circuit in the neighborhood of the switching pressure of the precontrol pilot valve. An unstable switching state renders the complete separation of the two user circuits from each other more difficult.
The device taught in the German Printed Patent Publication DE-OS 3,347,637 solves this general problem in that the precontrol pilot valve is provided with pressure-subjectable active transfer faces having different dimensions. Pressure is simultaneously applied to or released from, one of the active transfer faces of the precontrol pilot valve by the switch valve. The force application or the force release, respectively, acting thereby additionally on the precontrol pilot valve, allows the change between two stable switch positions.
Simultaneously, this additionally acting force also provides a measure for the pressure difference of the pressures in the primary circuit, at which pressures the precontrol pilot valve reverses its control state. It is a disadvantage in this context that, according to the German Printed Patent Publication DE-OS 3,347,637, the ratio of the active transfer faces and thus the effect of the active transfer faces onto the switching pressure difference of this device are prespecified. Therefore, adjustment possibilities of the switching range for balancing of construction tolerances which occur particularly in the size tolerance of the valve covering of the precontrol pilot valve and in the non-uniform characterizing curves of the springs, are not realizable with safety and certainty.
On the other hand, small switch and pressure differences can be implemented only with difficulty, since a safe change between the switching positions is not assured in case of too small a ratio of the active transfer faces relative to each other.
The German Printed Patent Publication DE-AS 1,233,223 to Jean Mercier teaches a pressure control valve for hydraulic plants. The reference teaches to use a cylindrical piston having a cylindrical section 24 and a conical section 25, where the conical part 24 forms a sealing face. The piston 23 forms the closure member of the relief valve V. The reference employs a storage container 10 and illustrates a line 18 connected to the pressure storage U. While the reference teaches a number of elements useful in fluid applications, it does not show control of a transfer to two different discharge locations depending on the prevailing pressure in one discharge location.
The German Printed Patent Publication DE-OS 3,327,978 to Jorg Dantlgraber teaches a device for the charging of a pressure means storage. However, the reference teaches that the control pressure depends on the pump pressure between two values. This device does not appear to be suitable for a switching dependent on the pressure value prevailing at one of two user locations to be alternatively supplied in fluid medium.
The German Printed Patent Publication DE-OS 3,208,831 to Glyn Philip Reginald Farr teaches a control valve for a motor vehicle hydraulic plant. The reference teaches that the switch-off pressure is determined by the face of a valve seat 29 of the valve 26. In view of the fixed size of such a valve seat, there is no practical possibility for adjusting the pressure inducing the relative switch pressure levels associated with the switching process.
The German Printed Patent Publication DE-OS 2,838,115 to Glyn Philip Reginald Farr teaches the use of a hydraulic pump, which suctions hydraulic fluid from a container, where a pressure storage is subjected to a pressure fluid and where the pump acts on a relief valve in a feed line between the pump and the pressure storage, such that the pressure storage is not overloaded and allows the pump to load the pressure storage again. It appears that this hydraulic system consequently does not provide for a transport to two receiving ports dependent on and controlled by the pressure level prevailing in one of the receiving ports.